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package javax.xml.xpath;

/**
 * <p>An <code>XPathFactory</code> instance can be used to create
 * {@link javax.xml.xpath.XPath} objects.</p>
 *
 * <p>See {@link #newInstance(String uri)} for lookup mechanism.</p>
 *
 * <p>The {@link XPathFactory} class is not thread-safe. In other words,
 * it is the application's responsibility to ensure that at most
 * one thread is using a {@link XPathFactory} object at any
 * given moment. Implementations are encouraged to mark methods
 * as <code>synchronized</code> to protect themselves from broken clients.
 *
 * <p>{@link XPathFactory} is not re-entrant. While one of the
 * <code>newInstance</code> methods is being invoked, applications
 * may not attempt to recursively invoke a <code>newInstance</code> method,
 * even from the same thread.
 *
 * @author <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @since 1.5
 */
public abstract class XPathFactory {


  /**
   * <p>The default property name according to the JAXP spec.</p>
   */
  public static final String DEFAULT_PROPERTY_NAME = "javax.xml.xpath.XPathFactory";

  /**
   * <p>Default Object Model URI.</p>
   */
  public static final String DEFAULT_OBJECT_MODEL_URI = "http://java.sun.com/jaxp/xpath/dom";

  /**
   * <p> Take care of restrictions imposed by java security model </p>
   */
  private static SecuritySupport ss = new SecuritySupport();

  /**
   * <p>Protected constructor as {@link #newInstance()} or {@link #newInstance(String uri)}
   * or {@link #newInstance(String uri, String factoryClassName, ClassLoader classLoader)}
   * should be used to create a new instance of an <code>XPathFactory</code>.</p>
   */
  protected XPathFactory() {
  }

  /**
   * <p>Get a new <code>XPathFactory</code> instance using the default object model, {@link
   * #DEFAULT_OBJECT_MODEL_URI}, the W3C DOM.</p>
   *
   * <p>This method is functionally equivalent to:</p>
   * <pre>
   *   newInstance(DEFAULT_OBJECT_MODEL_URI)
   * </pre>
   *
   * <p>Since the implementation for the W3C DOM is always available, this method will never
   * fail.</p>
   *
   * @return Instance of an <code>XPathFactory</code>.
   * @throws RuntimeException When there is a failure in creating an <code>XPathFactory</code> for
   * the default object model.
   */
  public static XPathFactory newInstance() {

    try {
      return newInstance(DEFAULT_OBJECT_MODEL_URI);
    } catch (XPathFactoryConfigurationException xpathFactoryConfigurationException) {
      throw new RuntimeException(
          "XPathFactory#newInstance() failed to create an XPathFactory for the default object model: "
              + DEFAULT_OBJECT_MODEL_URI
              + " with the XPathFactoryConfigurationException: "
              + xpathFactoryConfigurationException.toString()
      );
    }
  }

  /**
   * <p>Get a new <code>XPathFactory</code> instance using the specified object model.</p>
   *
   * <p>To find a <code>XPathFactory</code> object, this method looks the following places in the
   * following order where "the class loader" refers to the context class loader:</p> <ol> <li> If
   * the system property {@link #DEFAULT_PROPERTY_NAME} + ":uri" is present, where uri is the
   * parameter to this method, then its value is read as a class name. The method will try to create
   * a new instance of this class by using the class loader, and returns it if it is successfully
   * created. </li> <li> ${java.home}/lib/jaxp.properties is read and the value associated with the
   * key being the system property above is looked for. If present, the value is processed just like
   * above. </li> <li> Use the service-provider loading facilities, defined by the {@link
   * java.util.ServiceLoader} class, to attempt to locate and load an implementation of the service
   * using the {@linkplain java.util.ServiceLoader#load(java.lang.Class) default loading mechanism}:
   * the service-provider loading facility will use the {@linkplain java.lang.Thread#getContextClassLoader()
   * current thread's context class loader} to attempt to load the service. If the context class
   * loader is null, the {@linkplain ClassLoader#getSystemClassLoader() system class loader} will be
   * used. <br> Each potential service provider is required to implement the method {@link
   * #isObjectModelSupported(String objectModel)}. The first service provider found that supports
   * the specified object model is returned. <br> In case of {@link java.util.ServiceConfigurationError}
   * an {@link XPathFactoryConfigurationException} will be thrown. </li> <li> Platform default
   * <code>XPathFactory</code> is located in a platform specific way. There must be a platform
   * default XPathFactory for the W3C DOM, i.e. {@link #DEFAULT_OBJECT_MODEL_URI}. </li> </ol> <p>If
   * everything fails, an <code>XPathFactoryConfigurationException</code> will be thrown.</p>
   *
   * <p>Tip for Trouble-shooting:</p> <p>See {@link java.util.Properties#load(java.io.InputStream)}
   * for exactly how a property file is parsed. In particular, colons ':' need to be escaped in a
   * property file, so make sure the URIs are properly escaped in it. For example:</p>
   * <pre>
   *   http\://java.sun.com/jaxp/xpath/dom=org.acme.DomXPathFactory
   * </pre>
   *
   * @param uri Identifies the underlying object model. The specification only defines the URI
   * {@link #DEFAULT_OBJECT_MODEL_URI}, <code>http://java.sun.com/jaxp/xpath/dom</code> for the W3C
   * DOM, the org.w3c.dom package, and implementations are free to introduce other URIs for other
   * object models.
   * @return Instance of an <code>XPathFactory</code>.
   * @throws XPathFactoryConfigurationException If the specified object model is unavailable, or if
   * there is a configuration error.
   * @throws NullPointerException If <code>uri</code> is <code>null</code>.
   * @throws IllegalArgumentException If <code>uri</code> is <code>null</code> or <code>uri.length()
   * == 0</code>.
   */
  public static XPathFactory newInstance(final String uri)
      throws XPathFactoryConfigurationException {

    if (uri == null) {
      throw new NullPointerException(
          "XPathFactory#newInstance(String uri) cannot be called with uri == null");
    }

    if (uri.length() == 0) {
      throw new IllegalArgumentException(
          "XPathFactory#newInstance(String uri) cannot be called with uri == \"\"");
    }

    ClassLoader classLoader = ss.getContextClassLoader();

    if (classLoader == null) {
      //use the current class loader
      classLoader = XPathFactory.class.getClassLoader();
    }

    XPathFactory xpathFactory = new XPathFactoryFinder(classLoader).newFactory(uri);

    if (xpathFactory == null) {
      throw new XPathFactoryConfigurationException(
          "No XPathFactory implementation found for the object model: "
              + uri);
    }

    return xpathFactory;
  }

  /**
   * <p>Obtain a new instance of a <code>XPathFactory</code> from a factory class name.
   * <code>XPathFactory</code> is returned if specified factory class supports the specified object
   * model. This function is useful when there are multiple providers in the classpath. It gives
   * more control to the application as it can specify which provider should be loaded.</p>
   *
   *
   * <h2>Tip for Trouble-shooting</h2> <p>Setting the <code>jaxp.debug</code> system property will
   * cause this method to print a lot of debug messages to <code>System.err</code> about what it is
   * doing and where it is looking at.</p>
   *
   * <p> If you have problems try:</p>
   * <pre>
   * java -Djaxp.debug=1 YourProgram ....
   * </pre>
   *
   * @param uri Identifies the underlying object model. The specification only defines the URI
   * {@link #DEFAULT_OBJECT_MODEL_URI},<code>http://java.sun.com/jaxp/xpath/dom</code> for the W3C
   * DOM, the org.w3c.dom package, and implementations are free to introduce other URIs for other
   * object models.
   * @param factoryClassName fully qualified factory class name that provides implementation of
   * <code>javax.xml.xpath.XPathFactory</code>.
   * @param classLoader <code>ClassLoader</code> used to load the factory class. If
   * <code>null</code> current <code>Thread</code>'s context classLoader is used to load the factory
   * class.
   * @return New instance of a <code>XPathFactory</code>
   * @throws XPathFactoryConfigurationException if <code>factoryClassName</code> is
   * <code>null</code>, or the factory class cannot be loaded, instantiated or the factory class
   * does not support the object model specified in the <code>uri</code> parameter.
   * @throws NullPointerException If <code>uri</code> is <code>null</code>.
   * @throws IllegalArgumentException If <code>uri</code> is <code>null</code> or <code>uri.length()
   * == 0</code>.
   * @see #newInstance()
   * @see #newInstance(String uri)
   * @since 1.6
   */
  public static XPathFactory newInstance(String uri, String factoryClassName,
      ClassLoader classLoader)
      throws XPathFactoryConfigurationException {
    ClassLoader cl = classLoader;

    if (uri == null) {
      throw new NullPointerException(
          "XPathFactory#newInstance(String uri) cannot be called with uri == null");
    }

    if (uri.length() == 0) {
      throw new IllegalArgumentException(
          "XPathFactory#newInstance(String uri) cannot be called with uri == \"\"");
    }

    if (cl == null) {
      cl = ss.getContextClassLoader();
    }

    XPathFactory f = new XPathFactoryFinder(cl).createInstance(factoryClassName);

    if (f == null) {
      throw new XPathFactoryConfigurationException(
          "No XPathFactory implementation found for the object model: "
              + uri);
    }
    //if this factory supports the given schemalanguage return this factory else thrown exception
    if (f.isObjectModelSupported(uri)) {
      return f;
    } else {
      throw new XPathFactoryConfigurationException("Factory "
          + factoryClassName + " doesn't support given " + uri
          + " object model");
    }

  }

  /**
   * <p>Is specified object model supported by this <code>XPathFactory</code>?</p>
   *
   * @param objectModel Specifies the object model which the returned <code>XPathFactory</code> will
   * understand.
   * @return <code>true</code> if <code>XPathFactory</code> supports <code>objectModel</code>, else
   * <code>false</code>.
   * @throws NullPointerException If <code>objectModel</code> is <code>null</code>.
   * @throws IllegalArgumentException If <code>objectModel.length() == 0</code>.
   */
  public abstract boolean isObjectModelSupported(String objectModel);

  /**
   * <p>Set a feature for this <code>XPathFactory</code> and <code>XPath</code>s created by this
   * factory.</p>
   *
   * <p> Feature names are fully qualified {@link java.net.URI}s. Implementations may define their
   * own features. An {@link XPathFactoryConfigurationException} is thrown if this
   * <code>XPathFactory</code> or the <code>XPath</code>s it creates cannot support the feature. It
   * is possible for an <code>XPathFactory</code> to expose a feature value but be unable to change
   * its state. </p>
   *
   * <p> All implementations are required to support the {@link javax.xml.XMLConstants#FEATURE_SECURE_PROCESSING}
   * feature. When the feature is <code>true</code>, any reference to  an external function is an
   * error. Under these conditions, the implementation must not call the {@link
   * XPathFunctionResolver} and must throw an {@link XPathFunctionException}. </p>
   *
   * @param name Feature name.
   * @param value Is feature state <code>true</code> or <code>false</code>.
   * @throws XPathFactoryConfigurationException if this <code>XPathFactory</code> or the
   * <code>XPath</code>s it creates cannot support this feature.
   * @throws NullPointerException if <code>name</code> is <code>null</code>.
   */
  public abstract void setFeature(String name, boolean value)
      throws XPathFactoryConfigurationException;

  /**
   * <p>Get the state of the named feature.</p>
   *
   * <p>
   * Feature names are fully qualified {@link java.net.URI}s.
   * Implementations may define their own features.
   * An {@link XPathFactoryConfigurationException} is thrown if this
   * <code>XPathFactory</code> or the <code>XPath</code>s
   * it creates cannot support the feature.
   * It is possible for an <code>XPathFactory</code> to expose a feature value
   * but be unable to change its state.
   * </p>
   *
   * @param name Feature name.
   * @return State of the named feature.
   * @throws XPathFactoryConfigurationException if this <code>XPathFactory</code> or the
   * <code>XPath</code>s it creates cannot support this feature.
   * @throws NullPointerException if <code>name</code> is <code>null</code>.
   */
  public abstract boolean getFeature(String name)
      throws XPathFactoryConfigurationException;

  /**
   * <p>Establish a default variable resolver.</p>
   *
   * <p>Any <code>XPath</code> objects constructed from this factory will use
   * the specified resolver by default.</p>
   *
   * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code>
   * is <code>null</code>.</p>
   *
   * @param resolver Variable resolver.
   * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
   */
  public abstract void setXPathVariableResolver(XPathVariableResolver resolver);

  /**
   * <p>Establish a default function resolver.</p>
   *
   * <p>Any <code>XPath</code> objects constructed from this factory will
   * use the specified resolver by default.</p>
   *
   * <p>A <code>NullPointerException</code> is thrown if
   * <code>resolver</code> is <code>null</code>.</p>
   *
   * @param resolver XPath function resolver.
   * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
   */
  public abstract void setXPathFunctionResolver(XPathFunctionResolver resolver);

  /**
   * <p>Return a new <code>XPath</code> using the underlying object
   * model determined when the <code>XPathFactory</code> was instantiated.</p>
   *
   * @return New instance of an <code>XPath</code>.
   */
  public abstract XPath newXPath();
}
